There presently exist some products for performing the monitoring of equipment on an electrical network.
The system having the commercial denomination "MONITEQ" of the service company Hydro-Quebec, and the one called "INSITE".RTM. of the company Doble Engineering Company, are both monitoring systems for circuit breakers that use various sensors, among other things, for pressure and humidity measurements. The pressure measurement provides a part of the dynamic during the operation of the circuit breaker, but this measurement is very different from the acceleration: the approach used in both cases is not of a vibro-acoustic type (i.e. acoustic signature). The approach by the pressure measurement is not applicable on other switching equipments, such as tap changers or interrupters.
The product having the commercial denomination "LTC-MAP" of the company Harley.TM., and the one called "SENTRY".RTM. of the company QualiTROL.RTM. are intended for the transformer market, including tap changers, but not circuit breakers or interrupters. If they monitor several parameters like the position of a tap changer, the temperature differential and the motor's current, they however do not rely upon a vibro-acoustic approach, thereby leaving away a very appreciable diagnostic information source.
The company Programma also proposes a variety of circuit breaker monitoring and testing apparatuses. The following parameters are often tested on a circuit breaker: the closing and opening times, the resistance of the main contacts and the synchronisation of the contact operation, the contact travel and speed, etc. For this purpose, the measured values are compared to limit values specified by the manufacturer or values that have been established through experience by the organization in charge of the maintenance. In many cases, a signature consisting of different measurements taken when the circuit breaker is new is compiled. This signature can then be used as a reference for the subsequent measurements. Any noticed change clearly indicates a change in the condition of the circuit breaker. The tests are performed power-off. The system is not a monitoring system as such. It uses accelerometers temporarily mounted, for the test, on top of a power-off circuit breaker and relies upon a vibro-acoustic approach. However, the accelerometers must be positioned down the equipment, at the ground voltage, for the continuous monitoring of an interrupter. Since the distance between the sensor and the vibration source modifies the signal processing issue, a phase filter can be required to correct the phase dispersion amplified by a long path. The system of Programma extracts the time distorsion on the signature during a comparison with a reference signature, and uses this information for diagnostic purposes. However, the processing achieved by the system is based on the DTW (Dynamic Time-Warping) algorithm, known in the speech processing field, and which adjusts the signatures locally and not globally. The use of this algorithm provides a poorly reliable and poorly tolerant system with respect to, for example, the randomness of the electric arcing that is present under power-on conditions and of course absent under power-off conditions. Furthermore, the system of Programma does not provide for the possibility to work out means or averages since it measures the time distorsion without removing it from the signal; the signatures are not time realigned. In the absence of a mean, it is the dispersion of a signature (.apprxeq.30%) that will be indicative of the sensitivity of the method and not the dispersion of a mean of signatures. The reference signature is thus a prior signature or a typical signature for the type of equipment subjected to a test. Since the system of Programma compares raw signals and not envelopes, it cannot correct the time distorsion of a raw signal without altering its frequency content.
The international application published under the number WO 97/34161 in the name of ABB Research Ltd. shows an envelope analog (and not digital) extraction method depending upon a dimensionless calculation of a statistical excess T.sub.i including the constants N.sub.0 and N.sub.t, for an envelope (and not a vibration signal) sampled between 0.1 and 100 kHz. The system is designed to observe the signal in a 0-10 kHz band. Phenomenons that occur from 10 kHz are thus ignored, notwithstanding that a time realignment would be more accurate over 10 kHz. Furthermore, the system only carries out a first order time realignment, that is, a global alignment on the position of the signature. The method does not perform any interpolation, which limits the resolution of the realignment to the time sampling rate of 0.1 ms. The original mean is fixed. The acquisition duration of the system is merely in the order of 0.25 s while a longer duration (e.g. of more than 25 s) would allow to catch a wider market in the tap changers and the interrupters.
None of the known systems or apparatuses embodies vibro-acoustic signature treatment processes for tap changers nor interrupters. The processes intended for the circuit breakers are expensive and invasive.
One of the problems of the art resides in optimizing the parametrization of the comparison algorithm as a function of the signatures from different equipments.